target/arm: Use correct FPST for VCMLA, VCADD on fp16

target/arm: Use correct FPST for VCMLA, VCADD on fp16

When we implemented the VCMLA and VCADD insns we put in the
code to handle fp16, but left it using the standard fp status
flags. Correct them to use FPST_STD_F16 for fp16 operations.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20200806104453.30393-5-peter.maydell@linaro.org